Electrode rapping mechanism for electric precipitators



April 30, 1940.

G. H. HORNE ELECTRODE RAPPING MECHANISM FOR ELECTRIC PRECIPITATORS Filed March 29, 1938 4 Sheets-Sheet l '11.1111' lill/l Gero/ge ff. Hoff/e April 30, 1940- G. H. HoRNE 2.198.618

ELECTRODE RAPPING MECHANISM FOR ELECTRIC PRECIPITATORS Filed llaroh 29, 1938 4 Sheets-Sheet 2 9 J0 1 1 Q., 40 l j; 4a

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J6 -1|ll l 3 t' 21h 20 2] i l g I 2 j! 6i" Z o! 3! i J 2z .1 o a E 4O l Siwa/nim l f i George Af. Home l I April 30, 1940. H, HORNE 2,198,618

ELECTRODE'RAPPING MECHANISM FOB ELECTRIC PRECIPITATORS Filed March 29, 1938 4 Sheets-Sheet 25 Geary@ HHorrze APlll 30 1-940- G. H. HORNE 2,198,618

ELECTRODE RAPHNG MBcHANIsM FOR ELECTRIC PRECIPITATORS Filed March 29, 1938 4 Sheets-Sheet 4 :juwemhvn v Gear-ye ff. Horne Patented Apr. 30, 1940 ELECTRODE RAPPING INIEOHANISM FOB. ELECTRIC PRECIPITATORS George H. Horne, Glendale, Calif., assignor to Western Precipitation Corporation, Los Angeles, Calif., a corporation of California Application March 29, 193s, serial No. 198,789V

Claims.

The present invention is concerned with devices in electrical precipitators for mechanically operating hammers used to jar accumulated loose material from the electrodes.

I Rapping the electrodes with hammers or other similar means to jar of! the accumulations is normally carried out as an intermittent operation done at regular intervalsthat may vary in length from a few minutes to an hour or more in typical cases, depending on the rate of accumulation. The 'hammers are operated in some installations'by hand, but this is a dlmcult, tiresome Job and is usually done inemciently. When manual operation is reliedon, the intervals between rapping are frequently too long and the precipitator efllciency is lowered. .Also the expense is obiectionably high since a workman cannot do any other useful work in the intervals between the short periods of operation which seldom exceed from fifteen to thirty seconds.

Effective rapping requires a series of sharp, heavy blows of the hammers delivered against anvils associated with the electrodes, all blows being preferably of uniform weight. The period of contact of the hammer and anvil is also preierably as short as possible, because when grounded hammers are used to rap the high tension discharge electrodes, the electrodes are grounded and rendered inoperative while the hammer is in contact with the anvils. A rapid advance of the hammer followed immediately by a rapid reverse movement delivers the desired type ofsharp blow and also reduces to a minimum not only the time of contact and non-operation, but also the time that the hammers are within arcing distanceof the electrode. This characteristic of the hammer motion cannot be obtained in previous types or hammer operating mechanisms which have a rigid connection between the power source and o the hammer because the connecting linkage either holds the hammer against the electrode anvil for a short time which contact damps the vibrations set up in the-electrode, or else delivers an lneilective blow. v Mechanical hammer actuating mechanisms are preferably ilexible in use and operation so that they can b1:v installed on precipitators originally equipped with manually operated hammers and can in case of emergency be operated by hand. Also they should be easily adapted to automatic operation at predetermined regular intervals or at irregular intervals under the control of an operator.

4I'hus it is a general object of myinvention to provide a mechanism for operatingl hammers in a manner to deliver a short.'sharp blow that is effective to dislodge accumulated material and to keep the hammer in contact with the electrode anvils, or near it, for only a mlnimium length of time.

It is also a principal object to provide hammer operating mechanism that has a yielding or resilient connection at some point between the prime mover and the hammer in order to assure a quick return movement of the hammerand to easily regulate the strength of blow delivered.

Another object is to provide hammer operating mechanism in which the hammers return to a normal rest position out of contact with the anvils regardless of the position of the rest of the mechanism when rapping is stopped.

An additional object of my invention is to provide a mechanism for operating hammers that is adapted to swing hammers. against two anvils alternately and that is readily adjustable to equalize the strength of alternate blows and control the strength or weight of the blows.

A further object is to provide a hammer actuating mechanism that is easily and inexpensively built and operated either as an original installation or as an improvement to manually operated hammers.

It is also an object to provide in conjunction with a device for mechanically operating hammers, means operable by the device to reduce the current flow through the high tension discharge electrodes while they are being rapped.

These objects of my invention are accomplished by providing-in an electric precipitator having one or more electrodes associated with an anvil. one or more hammers adapted to be swung against the anvil, and hammer actuating mechanism comprising a driving member, a driven member, and a resilient connection between these two members. The driving member rotates or reciprocates and imparts a reciprocating motion te lthe driven member through .the resilient connection, which may be a pneumatic cylinder forml ing an air cushion. a spring. or other similar energy storing means. A connecting means, preferably articulated and inelastic, connects the driven member to the hammer to drive it, the hammer in my preferred form having an oscillating motion.

The strength of the blows delivered is regulated by means regulating the degree of compression of the resilient connection. thus a valve controlled uid lay-pass is used on the pneumatic cylinder and movable abutments are used with the springs.

When there are two spaced anvils in one precipitator, the hammers are mounted between the anvils and swing against the anvils alternately. Although the regulating means mentioned above can in some forms be used to atleast partially4 equalize the blows on both anvils, it is preferred in many instances to provide colmterbalancing means that is adJustable to fully equalize the impact on both anviis.

Because of the unusual and exacting requirements for a mechanism used to rap the high tension electrodes, I shall describe my invention in that aspect, but it will be readily apparent that the invention may be used equally well with hammers rapping the collecting electrodes since the general construction is very similar though the operating requirements are not as exacting.

How the above and other objects and advantages of my invention are attained will be more easily understood4 by reference to the followina description and the annexed drawings, in which:

Fig. 1 is a fragmentary view, partly in elevation and partly in vertical section as on line i-I of Fig. 2, of a typical electric precipitator showing hammer actuating mechanism constructed according to my invention;

Fig. 2 is a vertical section on line 2-2 of Fig. 1;

Fig. 3 is an enlarged fragmentary view illustrating in detail the construction of the pneumatic cylinder which is shown partially in elevation and partially in section;

Fig. 4 is an enlarged fragmentary section oi thel gas-tight bearing for the connecting rod attached to the hammer shaft;

Fig. 5 isa wiring diagram;

Fig. 6 is a vertical section of a variational form of resilient means comprising springs for driving the piston; and

Fig. 7 is an elevation partly in section of a variational form of pneumatic cylinder.

There is illustrated in Figs. 1 and 2 a portion of a typical, large scale electrical precipitator of the type used commercially to precipitate dust and other foreignparticles from a stream of gas; and the showing of this'particular precipitator is to be considered merely as illustrative of one application of my invention since the invention may be readily adapted to other types of precipi- -tator construction. The precipitator includes a4 structural frame indicated generally at I and a gas-tight housing attached to the frame members so that no gas will escape to the atmosphere as it passes through the precipitator for treatment. The collecting electrodes, which are grounded. may be of any suitable construction. but the rod-curtain.' type electrode |4 herein illustrated is typical of commercial practice and is composed of a row of vertically extending' rods l spaced at short intervals along angle I6 by which the rods are supported from one of the frame members I0. It will be understood that one unit of a precipitator normally includes a number of such collecting electrodes placed side 'by side and parallel to each other, but suitably spaced apart so that the dust-laden gas flows between the electrodes and in a direction parallel to their horizontal extent.

In each interval between two collecting elec trodes is located a high tension discharge electrode I3 which is composed of a number of fine wires I9 or sharp-edged rods supported from a pipe extending parallel to and midway between two collecting electrodes. Consequently, there are also a number of discharge electrodes, as may be seen from Fig. 2. all of similar construction and extending in the direction of gas flow. These collecting and discharge electrodes are opposed to each other and form together one section or unit of the entire precipitator. A number of such units may be placed lnseries so that the gas flows through them in succession; and Fig. l

vshows adjacent portions of two successive units.

Pipes 20 are bolted at each end to a channel 2|, and all the discharge electrodes of one unit are supported from a pair of channels 2| which each rest upon brackets 22 riveted to posts 24, of which there are two at each end oi' a unit though only one is shown. A pair of these posts 24 are supported from cross channel 25 which rests at each end upon a column of insulators 26 t0 electrically insulate the high tension disch 1'.; ge electrodes and their supporting -structures from the rest of the precipitator. Where .posts 2l and channel pass through openings in interior pantitions as at 21 and 28 respectively, means are provided for eliminating exposed sharp corners to prevent arcing over from the high tension parts to the grounded precipitator frame.

Although most-of the material precipitated out of the gas stream settles upon the collecting electrodes, yet a portion of the dust or foreign particles collects upon discharge wires or rods I9 of the high tension electrodes and it is necessary periodically to jar or vibrate these electrodes in order to free them of accumulated material that, if left on the electrodes, greatly reduces their electrical efficiency. In order to accomplish this jarring or rapping action, one or more disk-like hammers 30, attached to the ends of arms 3|, are swingingly supported from rock shaft 32 that extends parallel to channels 2|., Although one hammer 30 may be sufficient, it is preferred to provide several of them on a single shaft. Rock shaft 32 is rotatably mounted in bearing brackets 33 depending from frame members l0, and all the parts being normally of metal, the hammers arel grounded through the shaft and bearings. However, it is within the scope of my invention to make shaft 32 of electrically insulatinii material in whole or in part, or insulated from frame I0, in which case lthe hammers are not grounded and cannot short out the high tension electrode.

The rock shaft is so placed at one end' of a precipitator unit that, when it is rocked, hammers 30 swing upwardly and outwardly from their normal rest position below shaft 32 and strik'e 4against channels 2|, one hammer being shown at 30a in Fig. l at the time of contact with the right hand channel. The impact of the hammer blow against channel 2| jars all of pipes 20.

which rest on pins 2|a that are rigidly attached to the channel, and shakes the discharge wires I3 sufilciently to free them of accumulated material. When shaft 32 is placed mid-way between two units of the precipitator as shown' in Fig. l,

the same srt of hammers alternately strike against two channels 2|, one at each side of the shaft and belonging to different units.

Because channels 2| receive the blows deliveredby the hammers, these channels are termed anvils; but it will be realized that any suitable member associated ,with one or more electrodes in such a way as to transmit the blow to the electrodes when struck by a hammer may be used as an anvil and it is not necessary to use for this purpose one of the electrode supports. Anvils of the general type shown are used when a single anvil can be used to rap a series of electrodes. When the' hammer raps only one-elecu aisaeis 3 trode, it may strike against a portion of the electrode especially shaped or reinforced to re ceive the hammer impact; and this portion may be considered to be included in the scope of the term anvil as used herein. In either construction, the anvil is electrically part ofV the electrode because of the impracticability of electrically insulating the anvil from theelectrode.-

The resilient connection between the driving and driven member of the mechanism for actuating the hammers is pneumatic cylinder 34 which is illustrated in detail in Fig. 3. The cylinder comprises a cylindrical housing 34e closed at both ends by cylinder heads 35, the two heads being securely drawn down against the ends of housing 34a by nuts on the ends of tie rods 36 whichpass through the cylinder heads. Within cylinder 34 is the driven member. piston 31, which is provided at each face with a leather cup 38 to form a fluid-tight seal between the piston and the cylinder walls as the piston reciprocates within and relative to the cylinder. Piston rod 40 is attached to piston 31 by pins 4i and preferably extends through both, cylinder heads. This construction is preferred because it affords a double bearing for the piston rod and eliminates any tendency of the piston to-bind within the cylinder, and also because the net surface on each side of the piston exposed to air pressure within the cylinderis made equal.- Each cylinder head is supplied with a packing gland 42 through which piston rod slides.

For reasons that will be more evident. there is provided means for permitting restricted air flow between the chambers formed in the ends of the cylinder at the opposite sides of piston 31. 'I'his means preferably is in the form of an' external fluid by-pass 44 which is connected at each end to a fluid passage 46 in a cylinder head 35 that communicates with the cylinder interior in order that air may flow from one end of the cylinder, around piston 31, to the other end of the cylinder. A manually operable valve of any suitable conventional style is placed preferably in by-pass 44l so that the ow of fluid through the by-pass may be regulated or completely cut off as may be desired. Natural leakage of air around piston 31 may be relied on or a fluid passage may be placed in piston 31 instead, but the external passage. 44 is preferred because it is easily regulated in eil'ective size by an adjustable valve.

Cylinder 34 is connected at its upper end by bracket 48 to the outer end of the drive means, crank 49, which is rotated by drive shaft 50 of an electric motor 5l. Motor 5| is supported at the proper-height on a platformstructure 52 erected above the precipitator housing.

The lower end of piston rod 40 carries clevis 54 and pin 55 which pivotally joins the piston rod to the upper end of connecting rod 51. Connecting rod 51 has secured at its lower endfarm 5l which is pivotally connected at 59 to arm 30 on rock shaft 32. Piston rod 40. connecting rod 51, and arm 60 together/'10mn an inelastic articulated connecting means for drivingly connecting piston 31 to the hammers 30 so that reciprocation of the piston causes shaft .32 to rock and swing the hammers against anvils 2|, as will be more fully explained. y

From inspection of Fig. l Ait will be evident 'that the motion of the lower end of rod 51 has both horizontal and vertical components in the plane of the drawing. but that at a point near the upper end of the connecting rod this motion may be reduced to a vertical motion and a rocking motion about a horizontal axis perpendicular to the plane of the drawing. Advantage is taken oi' this fact to provide a gas-tight bearing and sealnear the upper end of the connecting rod where it passes through housing Il to the exteriorthereof. Connecting rod 51 is partly enclosed by portion Ila of the precipitator housing,

which is surmounted by casting 54. shown in greater detail in Fig. 4. The upper end of casting 64 has a vertical bore 65 across which extends cylindrical bearing 55. the bearing h aving a gastight fit with its cylindrical seat in casting 54 but being sufilciently free to. rock about its horizontal axis. Bearing 65 is held in place-against endwise movement by a removable plate 51 on the vertical face 'of casting 64. Rod 51 has a snug sliding fit within a vertically extending bore in bearing 66. This construction allows shaft 51 to move freely in a' longitudinaldirection and to rock about the axis of bearing 56 which seals the interior of the precipitator against gas loss around the exit of the connecting rod through the precipitator housing.

More satisfactory operation is obtained by using some equalizing or counterbalancing means to equalize the force supplied through connecting rod 51 on both up and down strokes. A preferred type of means for this purpose includes arm 10 mounted to swing about fulcrum 1| intermediatethe ends of the arm. At one side of the fulcrum 1|, arm 10 carries weight 12 slidingly mounted on the arm and provided with s'et screw 13 to lock the weight in any adjusted position. At the other side of the fulcrum. the arm is pivoted to the connection means between the piston and shaft 32, and this is easily accomplished by passing pin 55 of clevis 54 through the forked end of the arm, as illustrated in Fig. l3. The necessary longitudinal movement of arm-13 to accommodate the horizontal movement of pin 55 is afforded by placing fulcrum 1I at the upper end of post 15 which is pivotally mounted on bracket 15 secured to precipitator housing Il. Arm 10 may be used as a handle for operating the hammers' manually, valve 45 being opened to make the Work easier.

'Ihe operation oi the hammer actuating mechanism will be more readily understood if it is assumed that valve 45 of by-pass 44 is initially wide open so that air may flow freely from one end of cylinder 34 to the other end. Under these conditions, rotation of crank 43 by drive shaft 50 causes the pneumatic cylinder to reciprocate vertically with respect to piston 31. but the air withinr the cylinder displaced by the relative movement of piston 31 merely flows to the opposite end of the cylinder through the by-pass and no pressure is built up within the cylinder. The result is little or no vertical movement of piston 31 from its normal rest position and piston rod 40.merely swings about pin 55 which remains practically stationary, I

As valve 45 is slowly closed, the restriction to fluid flow through the by-pass causes the air in the lower portion of the cylinder to become compressed to some extent during the upward movement of the cylinder, and the air in the upper portion oi the cylinder to become equally compressed during the downward movement of the cylinder. The air pressure thus applied alternately to opposite faces of pisto'n 31 tends to drive itin thesaxne direction as'the cylinder, and thus raises and lowers rods 43 and 51. This reciprocating movement of the connecting rods rocksshaft 32 and swings hammers 33 from their ward stroke.

with one or both of anvils 2|, but no blow of any appreciable force is delivered.

When no counterbalancing means are provided, it would normally be found at this point that hammers 30 swing higher to the right in Fig. l than to the left, principally because the weight of the vertically moving parts 31, 40, 51, and 58 adds to the force of crank arm 49 on the down- The weight of cylinder 34 also adds to the force imparted by crank 48 on the down stroke in the same manner but to a smaller degree. It is to overcome this unbalanced effect that the counterbalancing means is provided; and, with the mechanism shown, the vertically reciprocating parts are counterbalanced by moving weight 12 out on arm 10 to the point at which hammers 30 swing equally to each side. The proper position for weight 12 is most readily determined if the weight is set when the hammers just contact anvils 2| at the end of each stroke.

Having made this adjustment, valve 45 is now closed still further to greatly restrict fluid flow in by-pass 44 and obtain the desired weight or strength of blow against anvils 2|. If leather cups 38 form an absolutely air-tight seal with the walls of the cylinder, then valve 45 will usually be slightly open when the desired force is obtained from hammers 30; but if there is a material amount of leakage past the piston, then this may be sufficient and valve 45 can be entirely closed without causing too heavy a blow.

The force of the blow delivered by the hammers is also controlled by both the speed of revolution and the throw of drive crank 49. Assuming the stroke of the piston to be equal to the maximum vertical movement of pin 59 and the frequency of reciprocation to be equal to the natural period of hammers 30, no impulse is delivered to the piston by movement of the cylinder except for the natural lag in movement of the hammer caused by friction' within the system. Under these circumstances there is almost no relative movement of the cylinder and piston and they move practically as a unit: and of course a minimum of energy is required since the only power consumed in keeping the hammers swinging at their natural period is that required to overcome friction losses. To increase the power delivered to the piston and correspondingly increase the energy of the hammer blows, either the stroke may be lengthened by changing the length of crankage or the frequency increased by changing the speed of motor 5|, or both.

In practice it has beenfound satisfactory to use a throw of crank 49 approximately equal to, but slightly greater than, the throw required were crank 48 connected rigidly to piston lrod 40, and a frequency approximately one-third greater than the natural period of the hammer. Since the piston reciprocates faster than the natural period of the rest of the system, the relative movement of the piston and cylinder compresses the ai-r between the piston and the cylinder ends. The energy stored in this compressed air is delivered to the piston and transmitted through the connection means 40, 51 and 60 to shaft 32 and hammers 30.' Naturally the cylinder always leads tle piston, so that at the moment of impact of the hammers the piston is already tending to reverse the direction of hammer movement and the sole energy of the blow delivered is from the compressed air and momentum of the hammers. The resilient connectionbetween the driven piston 31 and drive crank 43 afforded by the pneumatic cylinder eliminates any direct force from the driving member tending to hold the hammers in contact with the electrode anvils and consequently reduces the duration of contact between hammer and anvil to a-.minimum. Immediate disengagement of the hammer and anvil prevents any damping action by the hammer and allows the electrode to vibrate freely under the impact of the blow. The resilient connection also takes uplany over-travel of the cylinder caused by lt having a longer stroke than the piston.

Regardless oi' the position of crank 49 when the rapping action is stopped, hammers 30, because o f their weight, always return to their normal rest position shown by the full lines of Fig. l. Counterbalance 12 neutralizes. or approximately so, the effect of the weight of parts 40, 51, and 58 on the position of the hammers which thus assume substantially a position directly beneath shaft 32 and midway between anvils 2|. Leakage of air either through by-pass 44 or past piston 31 permits the weight alone of the hammers to move piston 31 and restore them to their rest position. This characteristic automatically insures that the hammers will not remain within arcing distance of the discharge electrodes or anvils `between periods of rapping.

As previously mentioned, hammers 30 are normally grounded to the frame of the precipitator whereas anvils 2| and the high tension electrodes are electrically insulated from the precipitator frame: but this is not the case during the short instant that the hammers contact the anvils, for during the contact the discharge electrodes are also grounded through the hammers. For this reason the duration of contact is made as short as possible because when so grounded therdischarge electrodes are rendered inoperative.

It is preferred to provide means for reducing the current in the high tension system during the period of rapping in order to reduce the tendency to arc over to the hammers as they approach and recede from the anvils, though such means can be omitted 'entirely if the hammers are used to rap low tension collecting electrodes. One arrangement for accomplishing this is illustrated in Fig. 5 in connection with a typical wiring diagram.l A transformer Il supplies high tension alternating current to rectifier Il which converts the current supplied to discharge electrode Il to unidirectional current. 'I'he collecting electrodes I4 are grounded. In the power supply circuit to the low tension side of transformer ll is an alternate branch circuit having a resistance I2 placed in parallel with the regular conductor Il, and switch 84 by which the power current may be supplied through either circuit branch I2 and I3.

Switch 54 is operated by relay 85 in the electric f circuit to motor 5| so that when motor 5| is running in order to drive the hammer actuating mechanism, relay moves switch I4 to the position shown to divert the transformer current through the resistance 82. When motor 5| is shut off, relay 85 ceases to operate and switch t4 automatically is returned to position to supply current through conductor B3. Though the relay shown is current operated, a voltage operated relay connected across the motor terminals can be used as weil. 'I'he electric circuit to motor 5| may be controlled by any type of switch mechanism either manually or automatically operated.

,to prevent binding.

readily adapted to mechanical operation so that the intermittent rapping operation may be automatically brought about after any desired interval of time.

Fig. 6 illustrates a variational form of mechanism to replace the pneumatic cylinder. in which springs are used instead of compressed air to ailord a resilient connection between the driving member, crank 49, and the driven member, the piston and piston rod 40. 'I'his mechanism comprises housing 88 within which piston 89 reciprocates, the piston being attached to rod 40 by a pin 90. On either side of piston 89 and bearing thereagainst is a compression spring 9| which is held within the cylinder by abutment plate 92. Plates 92 are preferably individually adjustable with respect to housing 88,.and for this purpose are here shown as threaded and screwed into an internal thread 88a in housing 88 so that the compression of each spring 9| can be individually adjusted. Lock nuts 93 hold abutment plates 92 in adjusted positions. Plates 92 also provide two spaced bearings for rod 4||and guide the piston Housing 88 is preferably a cylinder and closed at both ends in order to properly conne springs `9| and to exclude dirt from the springs and piston 89. However, an open cage may be used to connect the two abutments 92 if desired, and any other suitable form and shape may be given to the driven member 89. When the closed housing shown is used, it is preferred either to make piston 89 a loose fit in the cylinder or to provide ports 94 in the piston toY prevent compression of the air by the piston travel. Housing 88 is connected to crank 49 in the same way as cylinder 34, bracket 48a being suitably modified tc permit fastening it to the upper end of the housing.

The operation of the hammer is substantially the same as already described, the springs 9| being a resilient driving connection between drive crank 49 and driven piston 89 and one that stores energy in the same general manner asv the compressedlair at the endsof cylinder 34. Adjustment of the force of the strokes delivered to the driven member is accomplished by changing the positionl of abutments 92,-the length of threads 88a determining the range of adjustment; and if threads 88a are suiciently long, movement of the cylinder can be made to produce no movement of the piston, just as when valve 45 is fully open. Since plates 92 are individually movable, thecompression of springs 9| can be individually adjusted to make the force of the up and down strokes unequal and in this way some oi' the counterbalancing formerly done only by weight 12 can be done.

Fig. 'I illustrates a variational form of pneumatic cylinder equipped with two fluid by-pass lines 44, 44a controlled separately by a valve 4,5, 45a in each by-pass. In addition, each by-pss has a check valve 98, 98a of any conventional style. such as a ball or flap type, and so not shown in detail. As indicated by the arrows on the valves, air flow is in opposite direction in the two lines, as for example down only in the left hand o'ne and up only in the right hand one. By closing valves 45. 45a different amounts to produce unequal restriction to fluid' flow in the two by-pass lines. a greater pressure can be built up at ,one end of the cylinderthan at the other, and. neglecting other considerations, more force can be given to the piston on one stroke than the other. If right hapti valve 45a is closed more than the other valve 45, the upward movement of the cylinder produces a higher compression in the lower end of cylinder 34 than is produced in the upper end of the cylinder by its down- Award movement. rIfhe excess in the force thus consequently the force of the hammer blows ontheI two anvils can be regulated individually as desired, and can be made approximately equal, even without counterweight 12.-

Having described certain specific forms of my invention it will be understood that various changes in construction and arrangement of parts may be made without departing from the spirit and scope of my invention; and for this reason, the foregoing description is to be considered as illustrative of rather than restrictive upon the appended claims.

I claim:

1. In an electric precipitator having an electrode and an anvil associated therewith enclosed Within a gas-tight housing, externally actuated mechanism for rapping the anvil to jar loose precipitated material accumulated on the electrode, comprising a hammer mounted for movement into contact with the anvil from a normal rest position out of contact with the anvil; drive means; a driven member; resilient energy storing means, mounted exteriorly of the gas-tight housing and drivingly connecting the drive means and the driven member; articulated connection means connecting the drivenmember and the hammer to swing the latter against the anvil. said articulated connection means comprisinga lower rod and an upper rod pivotally connected to the lower rod; and a gas-tight bearing through which the lower. rod extends from the interior to the exterior of the housing; said lower rod being mounted for longitudinal and rocking movement in the bearing.

2. In an electric precipitator having a plurality oi' electrodes and a pair of spaced anvils associated therewith, mechanism for rapping the anvils to jar loose precipitated material accumulated on the electrodes, comprising a hammer disposed between the anvils and mounted to swing into alternate contact with the two anvils from a normal rest position oui'l of contact with either anvil; a pneumatic cylinder closed at both ends; a piston within the cylinder and movable relative thereto; drive means connected to and actuating the cylinder; connection means drivingly connecting the piston to the hammer to swing it against the anvils; and counterbalancing means attached -to said connection means for equalizing the blow of the hammer on eachl anvil.

3. In an electric precipitator having an electrode and an anvil associated therewith enclosed within a gas-tight housing, externally actuated mechanism for rapping'the anvil -to jar loose precipitated material accumulated on the electrode, comprising an anvil secured to an electrode; a hammer mounted for movement into contact with the anvil from a normal rest position out of contact with the anvil; a pneumatic cylinder closed at both ends 'and mounted exteriorly of the gas-tight housing; a piston within the cylinder and movable relative thereto; a rotatable crank connected to and reciprocating said cylinder relative to the piston to compress air between the piston and the ends of the cylinder;

and articulated connection means connecting the piston to the hammer to swing the hammer against the anvil, said articulated connection' means comprising a lo wer rod and an upper rod pivotally connected to the lower rod; and a gastight bearing through which the lower rod extends from the interior to the exterior of the gastight housing, said lower rod being mounted for longitudinal and rocking movement in the bearing.

4. In an electric precipitator, the combination of a high tension discharge electrode; an electrode anvil, a grounded hammer mounted on the precipitator frame and adapted to strike a blow against the anvil to jar the electrode, the hammernormally occupying a rest position out of contact with the anvil; means for actuating the hammer; an electric motor driving said hammer actuating means; a transformer supplying high tension current to the discharge electrode: a resistance in` an alternate branch of the low tension circuit of the transformer; and a relay operable by the power supply to the motor to divert the low tension circuit of the transformer through said resistance when the motor is driving the 'hammer actuating mechanism.

5. In an electric precipitator having a plurality of electrodes and a pair of spaced anvils associated therewith, mechanism for rapping the anvils to jar loose precipitated material accumulated on'the electrodes, comprising a hammer disposed between the anvils and mounted to swing into alternate contact with the two anvils from a normal rest position out of contact with either anvil; a pneumatic cylinder closed at both ends; a piston within the cylinder and movable relative thereto; drive means connected to and actuating the cylinder; connection means drivingly connecting the piston to the hammer to swing it alternately against the two anvils; and counterbalancing means attached to said connection vmeans for equalizing the blow of the hammer on each anvil, comprising a pivoted arm and a weight adiustably positioned on the arm.

6. In an electric precipitator having a plurality of electrodes and a pair of spacedanvils associated therewith, mechanism for rappingthe anvils to jar loose precipitated material accumulated on the electrodes comprising a hammer disposed between the anvils and mounted to swing into alternate contact with the two anvilsirom a normal rest position out oi' contact with either anvil; a pneumatic cylinder closed at both ends; a piston within the cylinder and movable relative thereto; drive means connected to and actuating the cylinder; a fluid by-pass interconnecting the ends of the cylinder at opposite sides of the piston: a valve in the by-pass adjustably restricting uid flow through the by-pass; and connection means drivingly connecting the piston to the algainst the two 8. In an electric precipitator having a plural-v y ity of electrodes and a pair of spaced anvils associated therewith, mechanism for rapping the anvils to jar the electrodes comprising a hammer disposed between the anvils and mounted to swing into alternate contact with the two anvils from a position out of contact with either anvil; a pneumatic cylinder closed at both ends; a piston within the cylinder and movable relative thereto;` drive means connected to and operable to reciprocate the cylinder; connection means drivingly connecting the piston to the hammer'to swing the hammer into alternateengagement with the respective anvils; two separate fluid bypass means each interconnecting the ends of the cylinder at opposite' sides of the piston; and independently adjustable valve means associated with each fluid by-pass means and operable individually to adjust the driving force exerted on the piston upon movement of the cylinder in each direction.

9. In an electric precipitator having a plurality of electrodes and a pair of spaced a'nvils associated therewith, mechanism for rapping the anvils to jar loose precipitated material accudrive means and the driven member; connection means drivingly connecting the driven member and the hammer to move the latter against the anvils, the connection means and the driven member being disposed to move`v generally vertically whereby the weight of the parts when moving downwardly increases the force oi' the blow against one anvil and when moving upwardly decreases the force of the blow against the other anvil; and counter-balancing means attached to said connection means and operating to exert a force opposing downward movement and assisting upward movement of the connection means and the driven member to equalize the blows on each anvil; said counter-balancing means including means for adjusting the counter-balancing force.

10. In an electric precipitator having a plurality of electrodes and a pair of spaced anvils associated therewith, mechanism for rapping the anvils to jar loose precipitated material accumulated on the electrodes, comprising a hammer disposed between the anvils and mounted to swing into alternate contact with the two anvils from a normal rest position out of contact with either anvil; a pneumatic cylinder; a piston reciprocable within the cylinder; a rotatable crank reciprocating the cylinder relative to the piston; a piston rod extending through one end of the cylinder and secured to the piston; connection means operatively connecting the piston rod to the hammer, the connection means and the piston rod being disposed to move generally vertically whereby the weight of the parts when moving downwardly increases the force of the blow against one anvily and when moving upwardly decreases the force o1' the blow against the other anvil; and counter-balancing means attached to said connection means and operating to exert a force opposing downward movement and assisting upward movement of the connection means and the piston rod to equalize the blows on each anvil,- said counter-balancing means including means for adjusting the counter-balancing force. 5

GEORGE H. HORNE. 

